Orthokeratology, also referred to as Night lenses, Ortho-K, OK, Overnight Vision Correction, Corneal Refractive Therapy (CRT), Accelerated Orthokeretology, Cornea Corrective Contacts, Eccentricity Zero Molding, and Gentle Vision Shaping System (GVSS), is the use of gas-permeable contact lenses that temporarily reshape the cornea to reduce refractive errors such as myopia, hyperopia, and astigmatism. [1]
Doctors discovered the reshaping phenomena of glass lenses as early as the 1940s. This history of orthokeratology includes contributions made by multiple authors to the use of contact lenses for myopia reduction. [2]
George Jessen created what was probably the first orthokeratology design in the 1960s made from PMMA material, which he marketed as "Orthofocus". These early designs had generally unpredictable results, leading to the belief that applied orthokeratology was more art or luck than science. Many groups and individuals claim to have been the first to develop modern orthokeratology solutions. However, Dr. Richard Wlodyga, Dr. Philip B. Hanisch and Nick Stoyan, in particular, are generally credited [3] with developing the first reverse zone lens design in the 1980s. [3]
However, it was not until computerized corneal topography became available during the 1990s that it became possible to apply the theory to create designs with repeatable results through being able to accurately map the surface curvature of the cornea using a non-invasive, painless imaging procedure. Additionally, the development of new base materials for rigid gas permeable lenses which provided much higher levels of oxygen permeability opened up the possibility of orthokeratology becoming an overnight procedure rather than being used for daytime wear alone. Finally, the introduction of computer-controlled precision lathes meant that lens designs could be manufactured to sub-micrometer levels of accuracy thereby offering the prospect of high volume production becoming commercially viable.[ citation needed ]
Nightwear ortho-k solutions were available to consumers in many countries outside the US much earlier than within the US, due to international differences between regulatory controls and bodies. In 1994, the FDA granted the first ever daily wear approval for a lens indicated for Orthokeratology to a type of lens called the Contex OK-Lens. In June 2002, the FDA granted approval for overnight wear of a type of corneal reshaping called "Corneal Refractive Therapy" (CRT), more than fifteen years after Europe. [4]
In the summer of 2000, at an educational meeting of optometrists in Toronto, the Orthokeratology Academy of America (OAA) was formed to support, promote and advance orthokeratology.[ citation needed ] In parallel, the British Orthokeratology Society (BOKS) was established in the UK with similar objectives to promote orthokeratology as a new procedure to correct myopia.[ citation needed ] The Orthokeratology Society of Oceania (OSO), formerly known as the Orthokeratology Society of Australia (OSA), is an Australia-based association of orthokeratology optometrists and researchers representing Australia and the South Pacific region.[ citation needed ]
In 2006 and 2007, papers presented at the British Contact Lens Association and the Global Orthokeratology Symposium indicated the possibility of orthokeratology slowing or stopping myopic progression. This was found to be effective in children in Hong Kong [5] and is the subject of wider study to verify this data. [6] Multiple other research evidence suggest that the reduction in myopic progression is roughly 50%, comparable to that of 0.01% atropine treatment, with remaining uncertainty regarding possible rebound effect after the Ortho-K use is discontinued. [7]
Tissue growth and propagation studies indicate that epithelial cells adjust growth in response to presence of a foreign material. CRT lens proximity to the cells therefore is thought to stimulate cell growth where less RoR proximity coincides with added growth and more proximity coincides with growth repression thereby creating a 'proximal pressure' on the epithelial cells. [8]
The orthokeratology website ortho-k.net explains in lay-terms that the mechanism behind ortho-k is that around 60% of the eye's focusing power is provided by the cornea, and this is extremely sensitive to very small changes: 6 μm flattening of corneal thickness (around 5% of the thickness of a human hair) results in 1 diopter of changed vision in myopia. [9] Therefore, a specially shaped lens can be used to lightly press the cornea, causing it gradually to be reshaped to the correct shape for focused vision. The corrective effect lasts up to 72 hours once initially acclimatized, which is long enough to be a practical means of eyesight correction. [10] There is some evidence (see above) that unlike other eyesight correction mechanisms, Ortho-K may also reduce future or ongoing eyesight changes or increased myopia, although this is still being researched.[ citation needed ]
Risks are comparable to or safer than ordinary contact lenses, since they are typically worn for much shorter periods (6–8 hours rather than daytime or 24/7) and while asleep rather than while active[ citation needed ]. They also compare favorably to surgical correction since no surgery is involved, corrections to the eye's shape can be handled over time (surgery corrects vision at a single point in time, but post-operative ongoing changes to eyesight will continue to occur during the patient's lifetime), and it is considered generally safe for younger patients[ citation needed ]. In addition, Ortho-K is broadly not 'new' from a safety viewpoint; contact lens safety generally speaking is considered to be well understood. However it is important, as with all contact lenses, to maintain good cleaning and hygiene discipline.[ citation needed ]
Rigid lenses are generally considered to be not as comfortable as soft lenses, but Ortho-K is claimed to avoid the feeling during waking hours of the eyelids moving over the lens edges while blinking. When Ortho-K lenses are worn, the eyes are closed for sleep, although the same issues that accompany wearing contact lenses during sleep (rapid eye movements and lower tear production) remain.[ citation needed ]
The cornea experiences a significant degree of adaptation within hours to days, although full adaptation often requiring 2 – 3 weeks. During this initial period vision may be affected for some people. Once adapted, FDA trials showed over 65% of patients achieved 20/20 eyesight and over 90% achieved 20/40 or better (the typical US requirement for driving without glasses). [11]
The corrective effect is stable but not permanent. Left to itself, the eye will slowly lose its adjusted shape, taking approximately 3 days to return to its former vision. [10] The Ortho-K lenses must therefore be worn regularly so the corrected corneal shape is preserved and maintained. Usually they are worn only for part of the day (typically only when asleep at night); some users may only need to use them one night out of every two or three nights. [10]
The US FDA overnight orthokeratology is approved up to -6.00 diopters of myopia and a maximum of 1.75 diopters of astigmatism.[ citation needed ]
In the United Kingdom, the procedure is offered primarily for myopic correction up to −5.00 diopters and up to −1.50 diopters of astigmatism. Fitting evidence for the leading lens designs indicates that procedures undertaken within these parameters have the highest probability of success. Some patients with higher degrees of myopia are successfully treated by specialist practitioners with "off-label" uses of these same lenses.
In South Africa, Australia and Taiwan, practitioners using the GOV orthokeratology system have achieved successful fits as high as −10.00D of myopia and +5.00D of hyperopia. Not every patient within these parameters will be suitable for the procedure and conditions such as flat or steep corneas may result in the procedure being less successful.[ citation needed ]
Counter-indications may include: [9]
During the first month of lens wear when the treatment zone on the surface of the cornea is in the process of becoming fully formed, some users may experience vision issues such as ghosting, double vision, contrast problems and/or starbursting, especially at night. These issues are generally resolved by the end of the first month of lens wear. If these issues persist beyond this initial period, the cause may be due to lack of centration of the lens on the eye and/or overly large pupil size (in light or dark). Resolution may be possible through redesign, material changes, better eye moisture retention (night eye masks, duct blocking, etc.) or other techniques.[ citation needed ]
Orthokeratology showed few severe side-effects, according to a March 2004 report of a very small sample of cases in China where supply of lenses at that time was not subject to any regulatory regime covering safety and efficacy. [12] [13] More typically, complications can occur due to the patient's failure to follow appropriate hygiene recommendations when handling or cleaning the lenses. One common issue being the use of tap water to rinse (although some systems allow for or suggest the use of "clean" tap water) or store as this may cause unwanted buildup of minerals on the contact as well as other issues. [14] [15] Complications may also be due to relative corneal hypoxia (lack of oxygen) with prolonged or overnight contact lens wear in lenses made from the wrong material. [16] However, the use of high or hyper oxygen-permeable materials as approved by the US Food and Drug Administration (FDA) significantly reduces hypoxia, and these are the materials that are normally used in orthokeratology.[ citation needed ]
Safety advice applicable to most modes of contact lens wear, also applies to ortho-k night-time lenses. An article in the January 2005 issue of Eye & Contact Lens: Science & Clinical Practice discusses two case reports of children who developed corneal ulcers when fit with Paragon CRT contact lenses, which were worn nightly. [17] Each patient presented with a bacterial corneal ulcer after wearing CRT contact lenses for less than 6 months. In the first patient, Pseudomonas aeruginosa was identified as the causative organism. In the second patient, Haemophilus influenzae was cultured from the ulcer. Both patients were treated with antibiotics, resulting in a rapid resolution of the corneal ulcers and preservation of vision. The writers conclude that "Paragon CRT lenses have been approved for use in patients of all ages. When used in children, these lenses may present unique problems. The absolute incidence of bacterial corneal ulcers in patients with CRT lenses are unknown. Severe caution should be used before prescribing CRT lenses for children and informed consent should include potential sight-threatening corneal ulcers." Although sight threatening corneal ulcers are rare, informed consent should routinely be obtained for all new contact lens wearers, whether worn overnight or not.[ citation needed ]
The Globe and Mail reported two cases in Canada in which Acanthamoeba infections during ortho-k treatment, possibly related to rinsing the lenses in tap water, led to temporary or permanent blindness. [18]
Orthokeratology lenses are made by a number of companies and all use special gas-permeable contact lenses to reshape the cornea. The lens material – and especially its oxygen permeability measured by its 'Dk' rating (the higher the value, the greater the degree of oxygen permeability) – is important for maintaining eye-health during the treatment.[ citation needed ]
Materials and methods vary globally, as does individual country approval. For example, lenses "Menicon Z Night" are generally used overnight only, but in USA they are also FDA-approved for up to 30-day wear, on a regular GP schedule.[ citation needed ]
Some practitioners have also designed their own orthokeratology lenses typically by using various software packages which combine corneal topographical data with the practitioners' own knowledge and experience to determine the appropriate lens parameters for individual patient prescriptions. These practitioners are obviously doing so "off-label" since their designs are not approved for safety by the FDA.
Contact lenses, or simply contacts, are thin lenses placed directly on the surface of the eyes. Contact lenses are ocular prosthetic devices used by over 150 million people worldwide, and they can be worn to correct vision or for cosmetic or therapeutic reasons. In 2010, the worldwide market for contact lenses was estimated at $6.1 billion, while the US soft lens market was estimated at $2.1 billion. Multiple analysts estimated that the global market for contact lenses would reach $11.7 billion by 2015. As of 2010, the average age of contact lens wearers globally was 31 years old, and two-thirds of wearers were female.
Myopia, also known as near-sightedness and short-sightedness, is an eye disease where light from distant objects focuses in front of, instead of on, the retina. As a result, distant objects appear blurry while close objects appear normal. Other symptoms may include headaches and eye strain. Severe myopia is associated with an increased risk of macular degeneration, retinal detachment, cataracts, and glaucoma.
Keratoconus (KC) is a disorder of the eye that results in progressive thinning of the cornea. This may result in blurry vision, double vision, nearsightedness, irregular astigmatism, and light sensitivity leading to poor quality-of-life. Usually both eyes are affected. In more severe cases a scarring or a circle may be seen within the cornea.
Far-sightedness, also known as long-sightedness, hypermetropia, and hyperopia, is a condition of the eye where distant objects are seen clearly but near objects appear blurred. This blur is due to incoming light being focused behind, instead of on, the retina due to insufficient accommodation by the lens. Minor hypermetropia in young patients is usually corrected by their accommodation, without any defects in vision. But, due to this accommodative effort for distant vision, people may complain of eye strain during prolonged reading. If the hypermetropia is high, there will be defective vision for both distance and near. People may also experience accommodative dysfunction, binocular dysfunction, amblyopia, and strabismus. Newborns are almost invariably hypermetropic, but it gradually decreases as the newborn gets older.
LASIK or Lasik, commonly referred to as laser eye surgery or laser vision correction, is a type of refractive surgery for the correction of myopia, hyperopia, and astigmatism. LASIK surgery is performed by an ophthalmologist who uses a femtosecond laser or a microkeratome to create a corneal flap to expose the corneal stroma and then an excimer laser to reshape the corneal stroma in order to improve visual acuity.
Presbyopia is physiological insufficiency of accommodation associated with the aging of the eye that results in progressively worsening ability to focus clearly on close objects. Also known as age-related farsightedness, it affects many adults over the age of 40. A common sign of presbyopia is difficulty reading small print which results in having to hold reading material farther away. Other symptoms associated can be headaches and eyestrain. Different people will have different degrees of problems. Other types of refractive errors may exist at the same time as presbyopia. This condition is similar to hypermetropia or far-sightedness which starts in childhood and exhibits similar symptoms of blur in the vision for close objects.
Photorefractive keratectomy (PRK) and laser-assisted sub-epithelial keratectomy (LASEK) are laser eye surgery procedures intended to correct a person's vision, reducing dependency on glasses or contact lenses. LASEK and PRK permanently change the shape of the anterior central cornea using an excimer laser to ablate a small amount of tissue from the corneal stroma at the front of the eye, just under the corneal epithelium. The outer layer of the cornea is removed prior to the ablation.
Refractive surgery is an optional eye surgery used to improve the refractive state of the eye and decrease or eliminate dependency on glasses or contact lenses. This can include various methods of surgical remodeling of the cornea (keratomileusis), lens implantation or lens replacement. The most common methods today use excimer lasers to reshape the curvature of the cornea. Refractive eye surgeries are used to treat common vision disorders such as myopia, hyperopia, presbyopia and astigmatism.
Refractive error is a problem with focusing light accurately on the retina due to the shape of the eye and/or cornea. The most common types of refractive error are near-sightedness, far-sightedness, astigmatism, and presbyopia. Near-sightedness results in far away objects being blurry, far-sightedness and presbyopia result in close objects being blurry, and astigmatism causes objects to appear stretched out or blurry. Other symptoms may include double vision, headaches, and eye strain.
A phakic intraocular lens (PIOL) is an intraocular lens that is implanted surgically into the eye to correct refractive errors without removing the natural lens. Intraocular lenses that are implanted into eyes after the eye's natural lens has been removed during cataract surgery are known as pseudophakic.
George Jessen (1916–1987) was an optometrist who was an early pioneer of the contact lens. He is credited with being one of the first to employ the concept of orthokeratology, a direct attempt to reduce refractive error with the use of a contact lens, under the term orthofocus.
Astigmatism is a type of refractive error due to rotational asymmetry in the eye's refractive power. This results in distorted or blurred vision at any distance. Other symptoms can include eyestrain, headaches, and trouble driving at night. Astigmatism often occurs at birth and can change or develop later in life. If it occurs in early life and is left untreated, it may result in amblyopia.
Automated lamellar keratoplasty (ALK), also known as keratomileusis in situ, is a non-laser lamellar refractive procedure used to correct high degree refractive errors. This procedure can correct large amounts of myopia and hyperopia. However, the resultant change is not as predictable as with other procedures.
Vision of humans and other organisms depends on several organs such as the lens of the eye, and any vision correcting devices, which use optics to focus the image.
Laser blended vision is a laser eye treatment which is used to treat presbyopia or other age-related eye conditions. It can be used to help people that simply need reading glasses, and also those who have started to need bifocal or varifocal spectacle correction due to ageing changes in the eye. It can be used for people who are also short-sighted (myopia) or long-sighted (hyperopia) and who also may have astigmatism.
Long-term contact lens use can lead to alterations in corneal thickness, stromal thickness, curvature, corneal sensitivity, cell density, and epithelial oxygen uptake, etc. Other changes may include the formation of epithelial vacuoles and microcysts as well as the emergence of polymegethism in the corneal endothelium. Decreased corneal sensitivity, vision loss, and photophobia have also been observed in patients who have worn contact lenses for an extended period of time. Many contact lens-induced changes in corneal structure are reversible if contact lenses are removed for an extended period of time.
The eye, like any other optical system, suffers from a number of specific optical aberrations. The optical quality of the eye is limited by optical aberrations, diffraction and scatter. Correction of spherocylindrical refractive errors has been possible for nearly two centuries following Airy's development of methods to measure and correct ocular astigmatism. It has only recently become possible to measure the aberrations of the eye and with the advent of refractive surgery it might be possible to correct certain types of irregular astigmatism.
The aim of an accurate intraocular lens power calculation is to provide an intraocular lens (IOL) that fits the specific needs and desires of the individual patient. The development of better instrumentation for measuring the eye's axial length (AL) and the use of more precise mathematical formulas to perform the appropriate calculations have significantly improved the accuracy with which the surgeon determines the IOL power.
Post-LASIK ectasia is a condition similar to keratoconus where the cornea starts to bulge forwards at a variable time after LASIK, PRK, or SMILE corneal laser eye surgery. However, the physiological processes of post-LASIK ectasia seem to be different from keratoconus. The visible changes in the basal epithelial cell and anterior and posterior keratocytes linked with keratoconus were not observed in post-LASIK ectasia.
Clear lens extraction, also known as refractive lensectomy, custom lens replacement or refractive lens exchange is a surgical procedure in which clear lens of the human eye is removed. Unlike cataract surgery, where cloudy lens is removed to treat cataract, clear lens extraction is done to surgically correct refractive errors such as high myopia. It can also be done in hyperopic or presbyopic patients who wish to have a multifocal IOL implanted to avoid wearing glasses. It is also used as a treatment for diseases such as angle closure glaucoma.